The various components of an optical recording apparatus belong to the prior art. They comprise a recording head including means for emitting a modulated light beam which carries information and a lens enabling the beam to be focused into a recording spot on a precise point of the carrier surface.
The recording spot generates the track outlining under the control of an advancing mechanism with a screw driven by a motor. The carrier itself is supported by a rotating turn-table.
By a recording process, for example etching by ablation the information is recorded along a track which may be in the form of a spiral consisting of equidistant turns or in the form of an array of concentric and equidistant circles.
Such an apparatus necessitates an advancing screw machined with a high degree of precision, because the movement of the recording head has to be uniform and progressive to ensure the equidistance of the turns of the track. The rotational speed of the carrier has to be completely uniform as well.
The advancing mechanism has to show a high level of mechanical stability. In order to prevent two successive turns from overlapping one another or at least from being hardly distinguishable during reading, the radial positional error in relation to the ideal outlining has to be less than 0.1 .mu.m for a track pitch of 1.6 .mu.m. Similarly, the turn-table supporting the carrier has to ensure perfect rotation thereof.